The aim of this research is to analyze the hormonal and behavioral factors which underlie maternal behavior in the rat. Hormonal factors arising during pregnancy, particularly the roles of estrogen and prolactin will be studied using hysterectomy, ovariectomy, hormone therapy, radioimmunoassays of ovarian hormones and gonadotrophins, and prolactin, and hypophysectomy. The role of olfaction in the maintenancy of postpartum maternal behavior will be studied as well as the development of maternal behavior in ontogeny and the neural site of action of estrogen.